if -fPIC error arises again, that's due to make clean needed

update also integration tests and iot examples

various language improvements to simplify packing/unpacking and
validation as well mapping simple conversion functions to table values

added high-level simple global functions to encrypt()/decrypt() which
execute KDF2 session and AES-GCM automatically by comparing headers.
Data format passed around is a table carrying the IV, header and checksum.

Also removed unuseful string tests: safe_string is now a local
function used internally, just checking for NULL or empty string.

There is still a problem when loading binary files where \0 may occur:
they get truncated when instantiated as Lua's string types. Should be
made octets directly.

also improved nodejs wrapper with hashbang and included examples
directory in distributed binaries.

will follow up with more helpers to simplify code

thanks to blended for the help testing

using cmsgpack_safe by antirez (same as used in redis)